Environment Report 2018

3.2. Produced Water When oil and gas are produced, water within the hydrocarbon reservoir is also brought to the surface. This produced water can make up over 95 per cent of produced liquids in some fields and is separated from the hydrocarbons before either being reinjected into the reservoir to provide reservoir support and maintain production, or treated and discharged to sea. Operators gain approval for produced water discharges by applying for a permit from OPRED. Produced Water Volumes The total amount of produced water handled on the UKCS follows the general trend of production and has therefore been declining since 2000 (see Figure 2). Over time, however, the decline in production has been greater than the decrease in produced water generated. This is because as the UKCS matures, hydrocarbons become harder to reach and extract and the process generates larger volumes of produced water per unit of production. Since 2014, the UKCS has reversed the production decline of the preceding 15 years, resulting in a rise in total produced water to 196 million cubic metres in 2017 (accounting for approximately 70 per cent of total well stream fluids). Despite this, the amount of produced water discharged to sea fell by 3 per cent, from 155 million cubic metres in 2016 to 143 million cubic metres in 2017. This is because record levels of produced water were reinjected into suitable sub-surface strata or reservoirs as an alternative to discharging to sea and, where technically feasible, to aid enhanced oil recovery (EOR). The amount of produced water reinjected to the subsurface increased to 53 million cubic metres last year, up 10 per cent from 2016.